Hi @Norbert_Hiller,
Thank you for your report and the team is sorry to hear that you’ve been experiencing a CG-NAT related blockage to port forwarding as a result of Deutsche Glasfaser’s dual-stack lite implementation.
As of now, ARC does not have an in-built mechanism for negotiating the address translation imposed by your ISP. However, as other users pointed out above, the Roon team is making excellent progress in testing IPv6 compatibility that should allow users in your situation to automatically configure port forwarding.
In the meantime, you’ll unfortunately need to rely on one of the workarounds posted in our #tinkering section, including Tailscale or other VPN options: Tailscale implementation with ARC to circumnavigate ISP CGNAT.
Please keep an eye on the main Deutsche Glasfaser tracking thread, as we will be posting updates there as soon as ARC has IPv6 compatibility available.